In recent years, a carbon dioxide capture and storage (CCS) technology for capturing and storing carbon dioxide (CO2) has been drawn attention as a countermeasure against global warming. In general, a comparatively large amount of carbon dioxide is generated in thermal power plants, steel plants, cement plants, and other chemical industry installations and the like, and the concentration of carbon dioxide in the exhaust gas is comparatively high. When the carbon dioxide capture technique is applied to such an installation, therefore, carbon dioxide can be captured efficiently.
The carbon dioxide capture technique as above is classified as a chemical absorption method. Specifically, exhaust gas is supplied to an absorber, in which carbon dioxide contained in the exhaust gas is absorbed in an absorbing liquid. In this instance, the exhaust gas from which carbon dioxide has been released is discharged from the absorber as a treated gas. The absorbing liquid having absorbed carbon dioxide is supplied to a stripper, in which the carbon dioxide is released from the absorbing liquid and is separated and captured. The absorbing liquid from which the carbon dioxide has been released in the stripper is returned into the absorber.
However, in the stripper it is difficult to completely release carbon dioxide from the absorbing liquid. Specifically, carbon dioxide in an amount determined by gas-liquid equilibrium in the stripper may remain in a dissolved state in the absorbing liquid (lean liquid). For this reason, depending on the gas-liquid equilibrium in the absorber, there may be a situation in which part of the carbon dioxide dissolved in the lean liquid supplied from the stripper to the absorber is released from the lean liquid. Therefore, there is a possibility that the concentration of carbon dioxide in the treated gas discharged from the absorber is raised and the carbon dioxide capture rate is lowered.